However, Akismet does require reliance on an external server / service. But I don't have a problem with that - it's been great, and with a very low failure rate.

Its a bit late right now, but I believe I witnessed a 'fond' post from Richard at punres with regard to Per Soderlind's akismet mod he is working on.   Akismet integration with a mod like this sounds pretty cool, to be sure, but people are still having some issues with it... need to get a leash on that automation yet (but it sure sounds promising)...

Regarding your actual question, after (getting bonked on the head and then) reading some about it I would have to admit the relevance (if indeed it is functioning with that virtual 'hive mind'-edness as you sort of put it); albeit then... the differences would (obviously) be (from what I could briely gather):
1) - akismet is (still) automated, and so it still requires regular human oversight anyway (but admittedly not a lot, as you and others interestingly keep pointing out),
2) - it relies on yet another spam-server of sorts basically, really,
3) - as well, what you point out in your comments (in post 53 above) regarding "controlling user registrations", 
...well it seems neither of these methods (live human or akismet) can really handle that right now...

   But I have to thank you for bringing my attention to this (again)... I bet between the two, akismet might have the upperhand to potentially be dealing with bogus sign ups, and that would really be something (but at what point do you arrive at being able to rely on that?  ;^)
   AND it is interesting, the way in which your, and others who are using akismet, comments I read are expressing their 'unique' pleasure with the product.

   After looking at it I still think there may be a value (viability worth testing) in a mod for punbb (or any forum) to allow a real-human collaborative system (internally) which does not rely on any automated system or other servers or more server overhead.  I wouldn't go so far as to argue one over the other mind you... I am only trying to look at the real similarities and difference, and saying I wonder if it may still be an unknown worth validating (just as askimet seems to be)?

Cheers,

Maybe I'm  not understanding correctly, but how is what you're describing different from Akismet?

Scot

   Maybe it would work something like this (and maybe this would be different?):
- Create criteria for allowing members who fulfill the criteria to join 'anti-spam moderator group'.
- Obviously it would have to be a system based in/on trust... (but consider, trust is a human characteristic bot-spam will probably never have or be able to emulate/automate (in our lifetimes anyway?), thus a system based in trust might well be a most powerful and simple tool (if we could figure out the best way to be leveraging that)...
- Those qulaifying to elect to volunteer to join this anti-spam moderator group would only have the responsibility and priviledges for deleting spam-posts, and possibly even spam-members (however you choose to set the criteria for that).  They would not have any other moderator priviledges.  (Some sort of checks and balances system could be discussed and sussed out for what might be the best ways for managing the members of this group, of course.)
- The idea here would be to enable the ability for the automated evolvement and maintenance of a virtual network of human thinking anti-spam tools (every fool is a tool, eh?).  (As opposed to the automated evolvement and maintenance of all sorts of blacklists and such (for ips, urls, words, ad nauseum) which isn't really so automated, because the minute you build something to think a certain way, it starts becoming outdated (but a basically intelligent human being seem sto always recognize what spam is or isn't ;^)...

It seems this is the sort of "feature-set" for a forum that would require very little:
- very basic modification to the forum itself,
- without requiring continual updates and maintenance of a/some utility(s) (because its not an anti-spam, or group of, anti-spam utilities, it would be a simple feature),
- as membership grows, the shear number of people-force would prpbably outweigh the ability of the  spam-bot force out there to be potentially overwhelming or taking down your system(?),
- and then who knows what other way-more simple protection tools might evolve to for enabling better leverage of/for the human driven anti-spam-moderator group?
- oh, and it may allow for additional usage of other existing anti-spam tools with less maintenance overhead?

???I wonder???

Does this really sound all that -stupid- or -unviable-?
Am I overlooking something obvious that renders this idea 'a non-idea'?  (Maybe this was thought out in the stone-henge days of anit-spam dev, and they tossed it because...?   
...added later-however, I know they're thinking about this art punres, because I just went there and read this http://www.punres.org/viewtopic.php?id=1848  ;^P
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What do you think? 
And if its a good idea, then maybe this feature capability should be built into 1.3, if only to facilitate the potential viability to prove itself out or not - lets see who uses it and how well it adapts to fighting spam?

Cheers,
Twohawks

PS: if you think I got my head up 'it', please be gentle pulling out, okay?

Yes I see why you shortened that :-D

I'm not sure I'm can tell my mods from my plugins. I just want to be able to install the board and touch it as little as possible after that. I guess I'm not exactly a power user ;-)

The extensions is a further step in that direction, with possibility to manipulate data all over the place ... and it will really "extend" the forum, so the name seems logical to me ...

http://punbb.org/forums/viewtopic.php?id=5936&p=1

Thanks.

Also I think someone else suggested the option to have unconfirmed accounts deleted after a certain number of days?

User Management plugin